Polycarbonate resins are widely used for producing molded articles because they are economical and relatively easy to mold. In addition, the resulting molded articles are lighter in weight and have better impact resistance than glass articles. However, because of insufficient surface hardness, such molded polycarbonate articles are susceptible to surface damage by contact, impact or abrasion with other objects. These polycarbonate articles are also susceptible to damage by light. Exposure to ultraviolet light for a long period of time typically causes the polycarbonate article to undergo discoloration, such as yellowing or fogging.
To improve the abrasion resistance and weatherability of the polycarbonate articles and of polystyrene and other articles, the surface of the article may be coated with an ultraviolet curable coating, such as an acrylate-based coating. These coatings typically contain a photoinitiator and an ultraviolet (UV) absorber. The UV absorber provides weathering protection to the underlying polycarbonate substrate and helps to prevent microcracking of the coating itself. However, as the amount of UV absorber in the curable coating increases, the curable coating tends to cure rather poorly, due in part to the absorption of a substantial portion of the curing radiation by the UV absorber and probably to migration of UV absorber to the coating surface during UV cure. At high concentrations, the absorber deprives the coating's photoinitiator of a portion of the ultraviolet energy necessary to properly cure the coating and detracts from the abrasion resistance of the coating surface.
It is an object of the present invention, therefore, to provide an ultraviolet curable coating containing a relatively large amount of UV absorber that is capable of being sufficiently cured. It is a further object of the present invention to provide an ultraviolet curable coating having excellent abrasion resistance and weatherability.